This invention relates to a hydrometallurgical method for the recovery of copper from copper sulphide minerals such as bornite, chalcocite, chalcopyrite, covellite and enargite.
Chalcopyrite is one of the most refractory copper sulphide minerals in relation to leaching in acidic ferric chloride and ferric sulphate systems at low temperature. This is exemplified by the mineral's slow leaching kinetics, which level off with time. This has been attributed to a process of “passivation”, but uncertainty in regard to the mechanism still remains.
It has been shown that the oxidative dissolution of chalcopyrite is a potential-dependent process and that the onset of “passivation” seems to occur at a surface potential (mixed potential) in excess of about 0.6 V (vs. SHE). Studies have also shown that under typical ferric leaching conditions, such as bioleaching and atmospheric leaching in ferric chloride and ferric sulphate systems, the mixed potential of the mineral is normally fixed in the so-called “passive region” of the anodic oxidation process, at conventional solution potentials in the region of 800 mV (vs. SHE) to 900 mV (vs. SHE), as measured against an inert platinum electrode. In this potential region, the mineral is subjected to the process of “passivation”, which is typified by the leveling-off of the leaching kinetics. This defines the fundamental problem of oxidative dissolution of chalcopyrite in such systems.
Many methods have been suggested to alleviate the problem of “passivation”, one of which is thermophile bioleaching at elevated temperatures. In one approach, bioleaching is carried out in a heap of low-grade, chalcopyrite-bearing ores. The process is operated in such a way that the heap temperature is raised sequentially from atmospheric to moderate thermophile or thermophile levels to achieve improved rates of chalcopyrite dissolution. The success of this strategy depends to a large extent on sufficient levels of available pyrite present in the ore and the successful oxidation thereof to achieve the required heat generation.
A number of prior art techniques have been proposed for the recovery of copper from chalcopyrite. These include the methods in:    (a) U.S. Pat. No. 6,277,341, wherein ferric sulphate is used as an oxidant and the surface potential of the chalcopyrite is controlled in the region of 350-450 mV (vs. SCE);    (b) WO03038137A, which describes a reductive process followed by an oxidative process, using at least ferric and oxygen to oxidize sulphur in chalcopyrite;    (c) a patent to UBC, which describes a chalcopyrite-concentrate leaching process with pyrite as a catalyst in a sulphate lixiviant, at a temperature in excess of 50° C.;    (d) a patent to CYPRUS, which describes the reaction of copper sulphate with chalcopyrite concentrate at elevated temperatures to form insoluble copper sulphide, soluble iron sulphate and sulphuric acid, and the leaching of copper sulphide with oxygen in an acid medium, or with ferric or cupric chloride or in an ammoniacal solution; and    (e) CL 40891 which relates to an agglomeration process, suited to supergene ores, with the addition of calcium chloride and stoichiometric quantities of acid. The chloride level is high and the solution is highly acidic.
The aforegoing review is principally in the context of chalcopyrite but similar considerations, to a greater or lesser extent, can be applicable to other copper sulphide minerals.
The recovery of copper from a low-grade, transitional and hypogene ore, which contains insufficient pyrite to generate a heap temperature for moderate thermophile, or thermophile bioleaching, remains problematic.
The invention aims to address, at least partly, this situation. The use of the invention is however not confined to these circumstances and may be extended to the leaching of high-grade concentrates at elevated temperatures.